Noob advice for 028 AV S rebuild

[ashbugwoody]

Bought this parts saw, owner said started on choke and stopped, wouldn't restart. I am a noob, 1st chainsaw rebuild, but not first 2 stroke rebuild. Found hole in brittle impulse line (pic). Piston shows wear but I can't catch a nail on any of the marks. Rings are free. No vac. test yet. I am thinking,
New seals - regardless of vac.
New impulse and fuel line
carb rebuild - regardless - Walbro
reuse piston and cylinder with new rings and cylinder clean up - if necessary
new wrist pin bearing?
Also, what is best lube for drive sprocket needle bearing?

What am I missing? Advice that will save me from failure? Also, safe mixture settings and break in technique, assuming things go as planned.

 

[motorhead99999]

If the piston doesn’t have skirt wear on it I would reuse it. Often if there isnt skirt wear the wrist pin and bearings should be fine. I usually use oem or caber rings and 028 s I usually build without the base gasket if I have enough squish tolerance to do so. Also make sure the plastic 90 on the carb isn’t cracked. Iv tore a couple apart a couple of times trying to figure out lean issues. Now it’s. The first thing I check

 

[ashbugwoody]

If the piston doesn’t have skirt wear on it I would reuse it. Often if there isnt skirt wear the wrist pin and bearings should be fine. I usually use oem or caber rings and 028 s I usually build without the base gasket if I have enough squish tolerance to do so. Also make sure the plastic 90 on the carb isn’t cracked. Iv tore a couple apart a couple of times trying to figure out lean issues. Now it’s. The first thing I check

Skirt on the exhaust side is marked (hard to see in pic) but cant feel grooves (yet). Probably will pull jug tonight. Also got new rubber intake for carb. How much squish are you looking for?

 

[dmb2613]

Piston looks too rough to reuse if you plan to run and work the saw

 

[SteveSr]

View attachment 867434View attachment 867436View attachment 867447View attachment 867449View attachment 867450
Bought this parts saw, owner said started on choke and stopped, wouldn't restart. I am a noob, 1st chainsaw rebuild, but not first 2 stroke rebuild. Found hole in brittle impulse line (pic). Piston shows wear but I can't catch a nail on any of the marks. Rings are free. No vac. test yet. I am thinking,
New seals - regardless of vac.
New impulse and fuel line
carb rebuild - regardless - Walbro
reuse piston and cylinder with new rings and cylinder clean up - if necessary
new wrist pin bearing?
Also, what is best lube for drive sprocket needle bearing?

What am I missing? Advice that will save me from failure? Also, safe mixture settings and break in technique, assuming things go as planned.

Based on the photos the top end is toasted, probably beyond reuse. Likely cause is the cracked impulse hose and subsequent air leak. This is likely a money pit unless you can find a good used OEM P & C for a reasonable price.

 

[SteveSr]

Bought this parts saw, owner said started on choke and stopped,

Now you know why it was a "parts" saw.

 

[Mad Professor]

P/C set NLA from stihl, piston i$ $$$ ($97). I'd do pres/vac test, clean it up, then pull cyl to see if it's salvageable. Looks of piston good chance cyl is O.K. with some work.

What does rest of saw look like? Clean and complete or filthy money pit? Post pictures.

 

[ashbugwoody]

P/C set NLA from stihl, piston i$ $$$ ($97). I'd do pres/vac test, clean it up, then pull cyl to see if it's salvageable. Looks of piston good chance cyl is O.K. with some work.

What does rest of saw look like? Clean and complete or filthy money pit? Post pictures.

I'll post more after pulling Jug tonight. The rest of the saw is really nice and the Stihl bar + chain is excellent. I don't have much in it over what the bar and chain is worth. The exhaust side piston wear looked not good to me but after feeling around with a plastic toothpick, I cant really feel anything that it hangs on below the rings. If the piston is toast, I'm hoping the cylinder is serviceable. we will see. I use another 028 for firewood and plan to use this one also.

 

[ashbugwoody]

Ok, so this is worse than I expected. Cylinder is trashed too. What do I need to look at on the bottom end, or is it time to fold em? If the bottom end isn't toast is Hyway viable? I don't see any used OEM P&C options on the web.

 

[RED-85-Z51]

Doesn't look bad, whats with the bore that you feel its trashed? I brought this 440 cylinder back from the dead with some emory cloth and a small hone.

Sent from my LM-G820 using Tapatalk

 

[ashbugwoody]

The cylinder has some gouges on the sprocket side between the exhaust and intake. To me, they seem too deep for a hone. I'll clean up and post a pic.

 

[SteveSr]

The cylinder has some gouges on the sprocket side between the exhaust and intake. To me, they seem too deep for a hone. I'll clean up and post a pic.

Hones are not recommended on Nikasil plated bores like these. The plating is only a couple of thou thick. A hone can ruin it in a heartbeat. You need to check the cylinder for any gouges through the plating. If found cylinder is trashed. Don't confuse aluminum transfer with gouges through the plating. It can be hard to tell sometimes.

 

[dmb2613]

I have a cheap 028 on the for sale side

 

[ashbugwoody]

After a closer look, this might be just aluminum transfer. Can be cleaned up with acid? Long wood q-tip, muriatic acid (straight), only dab on transfer spots and flush quick, scotchbrite rub after neutralizing each acid application. Am I on the right path? I don't want to screw up something that could be useable. Then what? Meteor piston? The piston definitely has some pretty deep scores.

 

[SteveSr]

After a closer look, this might be just aluminum transfer. Can be cleaned up with acid? Long wood q-tip, muriatic acid (straight), only dab on transfer spots and flush quick, scotchbrite rub after neutralizing each acid application. Am I on the right path? I don't want to screw up something that could be useable.

Acid can be problematic and high risk. If there are any holes in the plating or near a port edge acid will get under the plating and then it is Game Over. Less risky approach is with abrasives. Look for a @Mastermind Worksaws thread that describes the process. If you use a rotary tool and a split mandrel you still need to watch out for the port edges.

Then what? Meteor piston? The piston definitely has some pretty deep scores.

Existing piston is toast. Meteor is probably the best AM if it is available for your saw. Use OEM circlips if same size as the meteor or cut the ears off of the meteor. Install either type with the gap facing either up or down.

 

[ashbugwoody]

Acid can be problematic and high risk. If there are any holes in the plating or near a port edge acid will get under the plating and then it is Game Over. Less risky approach is with abrasives. Look for a @Mastermind Worksaws thread that describes the process. If you use a rotary tool and a split mandrel you still need to watch out for the port edges.


Existing piston is toast. Meteor is probably the best AM if it is available for your saw. Use OEM circlips if same size as the meteor or cut the ears off of the meteor. Install either type with the gap facing either up or down.

OK, I'm all in on the split mandrel, emory cloth and scotch brite. The video's are great. I'll be making my mandrels and s. brite holders first thing tomorrow. Thanks for this.

 

[drf255]

I use acid all the time. Just use eye protection, wear gloves, and apply with Qtip and watch. Use common sense. keep a bucket of warm baking soda solution nearby to dip and neutralize the acid on the jug.

Sand a bit and then keep repeating acid. Watch out by port edges, and watch out for areas that keep fizzing with not much apparent transfer-there could be a pit there.

I do acid and sanding together and end with scotchbrite. Sanding alone can polish transfer and not fully remove it in my limited experience. I will sometimes rub some acid over a final repair area and see if it reacts at all. Acid isn’t as perilous as some make it, you just need to pay attention. I wouldn’t soak a rag in acid and leave it in the jug overnight.

 

[Vintage Engine Repairs]

I have saved a number of cylinders with elbow grease. I’ll try a split mandrill next time. Only ever tried acid once and didn’t like the idea, both the dangers associated with it and the chance that it can eat away at the aluminium. 240 grit followed by 400 and I call it good when there is no more transfer. I use to use silicone carbide, but I think aluminum oxide will be a better option.

 

[ashbugwoody]

OK, I'm all in on the split mandrel, emory cloth and scotch brite. The video's are great. I'll be making my mandrels and s. brite holders first thing tomorrow. Thanks for this.

So, I got most of the transfer off using the emory and S Brite but I'm seeing a problem here. I know the pics make it hard to see but there is a score. Can you tell if this is terminal? I can feel it with my nail, a little bit, and I don't think it is likely to get much better even when 100% of the transfer is gone. BTW, thanks, the method does work really well.

 

[SteveSr]

So, I got most of the transfer off using the emory and S Brite but I'm seeing a problem here. I know the pics make it hard to see but there is a score. Can you tell if this is terminal? I can feel it with my nail, a little bit, and I don't think it is likely to get much better even when 100% of the transfer is gone. BTW, thanks, the method does work really well.

Not looking good in these photos. It looks like there are several places through the plating. It looks like something got in the cylinder and rattled around a bit. Were the rings, ring pins , and wrist pin circlips intact? Any detectable play in the crank bearings? Sometimes when the bearings start to come apart pieces of the retainer will break off and trash the cylinder. The other possibility is ingested garbage through the air intake.